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Thread: fluctuating PSI and unable to prime - replace pump/motor?

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    Join Date
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    SF Bay Area (Lamorinda), CA
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    fluctuating PSI and unable to prime - replace pump/motor?

    a while back I had posted about intermittent suction side air leaks that would cause our pump to lose prime. Hubby replaced the band connector seen in the upper right corner here:


    with a threaded fitting and union so it looks like this now:


    We also replaced the o-ring of the pump basket and things seemed to be looking good for about a week or so. Then yesterday afternoon I thought I'd run the pump a bit more b/c the water looked a little cloudy and I heard the unmistakable sound of a pump that lost prime. So I did the usual fill up the basket, add a bit more pool lube to the o ring, start pump and open bleed valve. The pump basket would fill up slowly and the PSI would go up but then before the water reached the lid, the PSI and water level would drop back down again.

    Is this a sign of a dying pump?

    If not, what could the problem be?

    If yes, what pumps would you recommend for an IGP of about 18K gallons with one skimmer, one return, one vacuum inlet (and suction control valves that have probably been frozen in place for a decade or more, so that the only way to divert more suction to the skimmer or the vacuum is to block the vacuum port or skimmer port), and equipment as listed in my siggy? Thanks!
    1950's-era 17K gallon formerly fiberglass, newly replastered IG rectangle (~15x30'),
    Hayward S244S Sand Filter with Franklin Electric 0.75 HP motor and WhisperFlo WFE-3 pump
    Clear ThermaTex bubble cover
    Manual vacuum

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    Re: fluctuating PSI and unable to prime - replace pump/motor?

    It could be your pump, but it could be some sort of blockage also that is preventing the full flow from being achieved.

    Have you inspected your pump impeller? That's what I would do first. You can probably free turn the impeller thru the basket inlet opening using your (small) hand and make sure it feels intact all the way around.

    Next, I would hook up a suction gauge to the pump basket's drain plug opening and check the suction reading to see if the pump is working ok. Something like this from harbor freight will do: http://www.harborfreight.com/fuel-pump- ... 93547.html

    Since you now have a threaded union in your suction line, you can try a test by hooking up a flexible 1 1/2" hose to the pump suction inlet and stick it in a kiddy pool or something to see if the pump primes and holds prime as you suck the water out of the kiddy pool.
    If this works, then you very likely have a problem with your copper suction line from your skimmer? Perhaps something is jammed in the line that got past an skimmer filter basket and/or float valve? Have you observed the skimmer while the pump is attempting startup? You could try some sort of back flush on the suction line by maybe hooking up a garden hose thru the threaded coupling and see if something comes out the other end.

    dave mc

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    Melt In The Sun's Avatar
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    Re: fluctuating PSI and unable to prime - replace pump/motor?

    A very simple thing to check (and probably the most common cause of intermittent priming problems) is low water level in the skimmer or a skimmer weir door that sticks closed occasionally. With either of those things, the pump can quickly empty the skimmer of water and start sucking air.
    11,200 gal, Pebble-Tec; Tristar 2-speed 1hp - Swimclear 325 ft2 cart - SWG - A & A in-floor cleaner - Heat pump. For the poolside cooking, a Yoder Wichita and a Big Steel Keg!
    TF Test Kits -- PoolMath -- Pool School
    Make each day your masterpiece. - John Wooden

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    Re: fluctuating PSI and unable to prime - replace pump/motor?

    Quote Originally Posted by Melt In The Sun
    A very simple thing to check (and probably the most common cause of intermittent priming problems) is low water level in the skimmer or a skimmer weir door that sticks closed occasionally. With either of those things, the pump can quickly empty the skimmer of water and start sucking air.
    Turned out it *was* low level in the skimmer (no weir to get stuck). It took a while for us to figure this out because when I'm in the shed looking at the filter basket, I have no idea what's happening out at the skimmer but when hubby was in the shed checking out the filter basket, I was hearing 'that giant sucking sound' at the skimmer. What was happening was that as soon as we bled out enough air for the pump to start building up suction, we'd get a vortex in the skimmer, air would go in, then the pump would lose suction and the water level in the skimmer would go back up again until we bled out enough air for there to be enough suction to start the vortex again. This hadn't been a problem at this level of water before but hubby's hypothesis is that when he changed out the connection to the pump, he increased the flow rate b/c the original connector had a smaller diameter.

    So our air leak problem appears to be solved at last.... but now I think we've got a slow water leak. ah, it's always something with these old pools, eh?
    1950's-era 17K gallon formerly fiberglass, newly replastered IG rectangle (~15x30'),
    Hayward S244S Sand Filter with Franklin Electric 0.75 HP motor and WhisperFlo WFE-3 pump
    Clear ThermaTex bubble cover
    Manual vacuum

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